Active noise cancellation circuits may be used in a variety of applications, such as personal communication systems, wireless communication devices, digital media players, and audio output devices, such as headphones. Active noise cancellation systems actively reduce acoustic noise of the environment by generating so-called “anti-noise” which may be the inverse form of the noise in the surrounding environment. Active noise cancellation systems generally comprise one or more microphones that capture environmental noise signals, a circuit that generates anti-noise, and one or more speakers to play the anti-noise in order to cancel the environmental noise. The anti-noise may destructively interfere with the surrounding environmental noise and thereby reduce the noise signal that reaches the ear of the user.
Conventional active noise cancellation circuits are often implemented via analog signal processing. This is because analog circuits have very short processing delays relative to digital circuits. However, analog signal processing has disadvantages in that it is difficult to make analog signal processing configurable or adaptive.
Active noise cancellation may be performed in the digital domain via signal filtering. The signal filtering may occur in stages that introduce different levels of filtering. Conventional filtering in digital active noise cancellation circuits may require memory-based delay circuits between the filter stages. These memory-based delay circuits can become very large in terms of memory space in the circuit, particularly when signals are oversampled.